Found out why one of my units was not hashing and having X's on the chips. Paste was everywhere on the inside. Even the screws holding the heat sink on had thermal paste on them.
Thanks for sharing this. How did you rectify the excess paste, and what was the impact on hashing performance of that unit?(Looks like now that BITMAIN has a heatsink also on the component side, this creates an 'opportunity' for this sort of problem)
Cheers